[QTMOKO] GPS pedometer app up on github

[Jim Morris]

Jim Morris wrote:
> I have checked in my very recent attempt to write a GPS based pedometer for Qtmoko.
> It is at http://github.com/wolfmanjm/qtpedometer
> 

There is a serious accuracy problem with determining the distance traveled during a trip.

I did some research, and there does not seem to be a consensus on how to do it, and the GPS device 
manufacturers obviously have proprietary solutions they do not disclose or discuss.

All the open source programs I looked at do it the simple but very inaccurate way I first tried. 
They basically calculate the distance between successive fixes (segments) and accumulate that as the 
distance. This has about a 20%-50% error (estimated).

The next attempt I discovered on the web (and how I do it now) is non-intuitive, but basically you 
take the current speed, and multiply it by the delta time since the last update. This is much more 
accurate, but still accumulates errors even if you are standing still it accumulates a small error. 
It works really well when driving though, but for walking (and I suspect biking), it is still 
inaccurate.

Next I added a speed threshold, which you must go over before the distance will accumulate, for 
walking I set that to .4 miles per hour or 0.1788159993648455703 meters per second.

This works well if you are standing still, as it does not accumulate any distance, but it increased 
the error significantly on a driving trip, when I compared the trip distance of my cars GPS with my 
version. I haven't tried a walking test yet.

So if anyone has any ideas how to make this more accurate I would welcome suggestions.

Thanks
Jim

-- 
Jim Morris, http://blog.wolfman.com